Constant Air Volume
How does CAV differ from VAV?
CAV keeps airflow constant and varies temperature; VAV keeps temperature constant and varies airflow.
Why is CAV less common in new builds?
VAV offers superior zone control and lower energy consumption, replacing CAV in most modern multi-zone applications.
What is a CAV unit in ducts?
A self-powered flow controller (resembling a butterfly valve) that maintains a fixed air flow rate in supply/return ducts regardless of pressure changes.
Constant Air Volume (CAV) is an HVAC system type where the supply air flow rate remains constant while the supply air temperature is varied to meet a space’s thermal loads. The fan operates at a fixed speed, delivering a steady volume of air (measured in CFM); room temperature is controlled by adjusting coil temperature based on thermostat readings, making it ideal for single-zone areas with stable loads.
In shop floor maintenance, CAV systems are applied in single-zone areas with stable thermal loads, such as manufacturing bays or warehouses. The fan runs continuously at full speed, delivering a constant air volume (CFM) while the supply air temperature is adjusted via heating or cooling coils based on thermostat readings. This simplicity reduces control complexity but leads to high energy consumption and wear on fan motors. Common issues include premature bearing failure from constant operation, over-conditioning in zones with reduced occupancy causing energy waste, and duct pressure imbalances in multi-zone setups leading to air starvation or over-pressurization. Proper calibration of dampers and regular motor maintenance are critical to mitigate these failures.
Fan motor wear from running continuously at full speed, leading to premature bearing failure and high energy use.
Over-conditioning (excessive reheating or cooling) in zones with reduced occupancy due to inability to modulate airflow, causing energy waste and comfort issues.
Duct pressure imbalance or damper improper calibration in multi-zone setups, resulting in air starvation in some rooms and over-pressurization in others.